Davekro,

Virtually all AV receiver manufacturers specify not using impedance loads of less than 6 ohms in order to comply with the UL and CSA product testing, and also to err on the side of caution. Some brands include an impedance switch that actually limits the power output and current flow to a lower impedance load to prevent the output devices from running too hot. Doing that also reduces the available power output dramatically into a 4-ohm load.

In the real world, however, some amplifier sections of some AV receivers tend to be more stable than others driving 4-ohm loads, Denon and Sherwood Newcastle being a couple that Axiom has had long experience with. Some other brands, as I've previously noted in the forums, have overly sensitive protection circuitry that immediately upon sensing greater current flow or increased heat from the output transistors, will shut down the AV receiver or put it into "current limiting", a mode that limits power output.

Also, it is not the number of midrange drivers and tweeters that will determine the timbral (tonal) balance of a loudspeaker. Using dual midranges and dual tweeters in the M80 gives it huge power handling in large rooms. It is subtle adjustments in crossover design and driver selection (among many factors) coupled with careful anechoic measurements and listening tests that will ultimately determine the tonal balance and neutrality of a loudspeaker. Over the years, I've tested some small bookshelf speakers from other manufacturers that are almost unlistenable because of excessive treble emphasis and wonky tonal balance.

Actually, in double-blind tests, the M80 is a slight bit smoother on female and male vocals than the M60. These differences are tiny, barely noticeable except in the instantaneous switching between the two speakers. You'll be fine with the M60s in your size of room and as other M60 owners have noted, they are capable of very loud, clean playback in very large spaces.

Also, your notion that sound from the rear speakers has to "travel" a long way--16 feet--to your listening area is not a significant factor. Sound travels at one foot per millisecond, so the sound from the rears in your room would take 16 milliseconds--that is 16/1,000ths of a second--to reach your ears. The setup on your Denon will insert digital delay quite a bit longer than that to prevent your ear/brain from hearing the rear surround signals before the sound from the front speakers.

Regards.

Alan

Alan Lofft,
Axiom Resident Expert (Retired)